[3.16.y-ckt stable] Patch "crypto: algif_skcipher - Fix race condition in skcipher_check_key" has been added to the 3.16.y-ckt tree

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    crypto: algif_skcipher - Fix race condition in skcipher_check_key

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt25.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

---8<------------------------------------------------------------

>From 7dffe6c5be4df3586261c181819f79b257e29d93 Mon Sep 17 00:00:00 2001
From: Herbert Xu <herbert at gondor.apana.org.au>
Date: Fri, 15 Jan 2016 22:02:20 +0800
Subject: crypto: algif_skcipher - Fix race condition in skcipher_check_key

commit 1822793a523e5d5730b19cc21160ff1717421bc8 upstream.

We need to lock the child socket in skcipher_check_key as otherwise
two simultaneous calls can cause the parent socket to be freed.

Signed-off-by: Herbert Xu <herbert at gondor.apana.org.au>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 crypto/algif_skcipher.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/crypto/algif_skcipher.c b/crypto/algif_skcipher.c
index de514c5d4503..45fa6bd9187b 100644
--- a/crypto/algif_skcipher.c
+++ b/crypto/algif_skcipher.c
@@ -551,22 +551,23 @@ static struct proto_ops algif_skcipher_ops = {

 static int skcipher_check_key(struct socket *sock)
 {
-	int err;
+	int err = 0;
 	struct sock *psk;
 	struct alg_sock *pask;
 	struct skcipher_tfm *tfm;
 	struct sock *sk = sock->sk;
 	struct alg_sock *ask = alg_sk(sk);

+	lock_sock(sk);
 	if (ask->refcnt)
-		return 0;
+		goto unlock_child;

 	psk = ask->parent;
 	pask = alg_sk(ask->parent);
 	tfm = pask->private;

 	err = -ENOKEY;
-	lock_sock(psk);
+	lock_sock_nested(psk, SINGLE_DEPTH_NESTING);
 	if (!tfm->has_key)
 		goto unlock;

@@ -580,6 +581,8 @@ static int skcipher_check_key(struct socket *sock)

 unlock:
 	release_sock(psk);
+unlock_child:
+	release_sock(sk);

 	return err;
 }